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mm/thp: make is_huge_zero_pmd() safe and quicker
commit3b77e8c8cd
upstream. Most callers of is_huge_zero_pmd() supply a pmd already verified present; but a few (notably zap_huge_pmd()) do not - it might be a pmd migration entry, in which the pfn is encoded differently from a present pmd: which might pass the is_huge_zero_pmd() test (though not on x86, since L1TF forced us to protect against that); or perhaps even crash in pmd_page() applied to a swap-like entry. Make it safe by adding pmd_present() check into is_huge_zero_pmd() itself; and make it quicker by saving huge_zero_pfn, so that is_huge_zero_pmd() will not need to do that pmd_page() lookup each time. __split_huge_pmd_locked() checked pmd_trans_huge() before: that worked, but is unnecessary now that is_huge_zero_pmd() checks present. Link: https://lkml.kernel.org/r/21ea9ca-a1f5-8b90-5e88-95fb1c49bbfa@google.com Fixes:e71769ae52
("mm: enable thp migration for shmem thp") Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Yang Shi <shy828301@gmail.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Jan Kara <jack@suse.cz> Cc: Jue Wang <juew@google.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Miaohe Lin <linmiaohe@huawei.com> Cc: Minchan Kim <minchan@kernel.org> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Peter Xu <peterx@redhat.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Wang Yugui <wangyugui@e16-tech.com> Cc: Zi Yan <ziy@nvidia.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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2 changed files with 11 additions and 2 deletions
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@ -297,6 +297,7 @@ struct page *follow_devmap_pud(struct vm_area_struct *vma, unsigned long addr,
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extern vm_fault_t do_huge_pmd_numa_page(struct vm_fault *vmf, pmd_t orig_pmd);
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extern struct page *huge_zero_page;
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extern unsigned long huge_zero_pfn;
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static inline bool is_huge_zero_page(struct page *page)
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{
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@ -305,7 +306,7 @@ static inline bool is_huge_zero_page(struct page *page)
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static inline bool is_huge_zero_pmd(pmd_t pmd)
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{
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return is_huge_zero_page(pmd_page(pmd));
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return READ_ONCE(huge_zero_pfn) == pmd_pfn(pmd) && pmd_present(pmd);
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}
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static inline bool is_huge_zero_pud(pud_t pud)
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@ -451,6 +452,11 @@ static inline bool is_huge_zero_page(struct page *page)
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return false;
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}
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static inline bool is_huge_zero_pmd(pmd_t pmd)
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{
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return false;
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}
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static inline bool is_huge_zero_pud(pud_t pud)
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{
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return false;
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@ -61,6 +61,7 @@ static struct shrinker deferred_split_shrinker;
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static atomic_t huge_zero_refcount;
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struct page *huge_zero_page __read_mostly;
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unsigned long huge_zero_pfn __read_mostly = ~0UL;
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bool transparent_hugepage_enabled(struct vm_area_struct *vma)
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{
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@ -97,6 +98,7 @@ static struct page *get_huge_zero_page(void)
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__free_pages(zero_page, compound_order(zero_page));
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goto retry;
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}
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WRITE_ONCE(huge_zero_pfn, page_to_pfn(zero_page));
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/* We take additional reference here. It will be put back by shrinker */
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atomic_set(&huge_zero_refcount, 2);
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@ -146,6 +148,7 @@ static unsigned long shrink_huge_zero_page_scan(struct shrinker *shrink,
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if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) {
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struct page *zero_page = xchg(&huge_zero_page, NULL);
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BUG_ON(zero_page == NULL);
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WRITE_ONCE(huge_zero_pfn, ~0UL);
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__free_pages(zero_page, compound_order(zero_page));
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return HPAGE_PMD_NR;
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}
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@ -2058,7 +2061,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
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return;
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}
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if (pmd_trans_huge(*pmd) && is_huge_zero_pmd(*pmd)) {
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if (is_huge_zero_pmd(*pmd)) {
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/*
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* FIXME: Do we want to invalidate secondary mmu by calling
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* mmu_notifier_invalidate_range() see comments below inside
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